THE VERTEBRATES 441 



some hoofed animals develop as a woolly coat, as in sheep, 

 goats, American bison, and Persian lamb. 



(14) Adaptations for special methods of locomotion are 

 very common among mammals. Examples are : kangaroos 

 for jumping, sloths for hanging from under side of branches 

 of trees, horses for running on solid ground, seals and whales 

 for swimming, bats for flying, and many mammals of different 

 orders for climbing. 



Many other interesting adaptations of mammals may 

 be found described in books on natural history. 



362. Economic Relations of Mammals. No other class 

 of animals approaches that of the mammals in economic 

 importance. The truth of this statement will be obvious 

 to any one who considers the vast monetary value of the 

 common domesticated mammals horses, cattle, sheep, pigs, 

 goats, and dogs. Also, in some countries, camels, elephants, 

 llamas, and reindeer are important domesticated mammals. 



The domesticated species are useful in (1) the human food- 

 supply, and (2) as beasts of burden. 



Many wild mammals are also useful to man. The most 

 valuable of these are the fur-bearers (chiefly carnivors, 

 such as seals, foxes, mink, bear). Whales have long been 

 hunted for the whale-bone obtained from their jaws and the 

 sperm-oil from their " blubber." A large whale of one species 

 may yield over $10,000 worth of whalebone and three hun- 

 dred barrels of oil. Elephants and walruses have been ruth- 

 lessly hunted for the ivory of their tusks. Sea-cows are 

 hunted for their flesh, oil, and hides. Beavers have been 

 nearly exterminated because of their valuable skins. 



Modern methods have made it possible to utilize every 

 particle of mammals slaughtered for human food. In ad- 

 dition to the meat obtained, the poorer qualities of fat are 

 made into soap ; the horns into combs ; the hoofs into glue ; 

 the best hair into packing for many purposes and the poorer 

 grade is used in plastering walls of buildings ; gelatin is made 



